1. Field of the Invention
The present invention relates to an apparatus and method for ablating biological tissue. In particular, the present invention relates to a catheter and a method of using a catheter including a bundle of optical fibers defining an ablation area at the distal end thereof. The entire bundle of optical fibers at the distal end of the catheter is deflectable with respect to a guidewire lumen so that a constant fluence is maintained over the ablation area.
2. Description of the Related Art
Numerous devices are known for using light energy to ablate an obstruction, such as plaque and thrombus, in a patient's body cavities or vessels. For example, U.S. Pat. No. 4,686,979 to Gruen; U.S. Pat. No. 5,188,632 to Goldenberg; and U.S. Pat. No. 5,041,108 to Fox et al. each disclose a laser catheter for ablating tissue in a body. In these devices, light energy is emitted from the distal end of the catheter by a plurality of optical fibers extending therethrough. The distal ends of the optical fibers define an ablation area, which is an area where tissue is ablated by the light energy emitted from the optical fibers. The amount of light energy emitted by the optical fibers per unit area is referred to as the fluence. To ablate obstructions in a cavity or vessel, it can be appreciated that catheters having small diameters are preferred because they can be inserted through smaller blood vessels and are less cumbersome to manipulate.
It is also known to deflect the distal ends of the optical fibers away from the path of the catheter so that the light energy emitted from the distal end of the fibers can be aimed at the tissue to be ablated. A common method for deflecting the distal ends of the optical fibers is to deflect the entire distal end of the catheter. For example, U.S. Pat. No. 5,188,632 to Goldenberg; U.S. Pat. No. 5,111,403 to Clarke et al.; U.S. Pat. No. 5,029,588 to Yock et al.; and U.S. Pat. No. 4,966,596 to Kuntz et al. each disclose a laser catheter having at least one inflatable balloon at or near the exterior surface at the distal end of the catheter. Inflating the balloon within a blood vessel, for example, forces the balloon against the wall of the vessel thereby moving the entire distal end of the catheter--including a guidewire and/or guidewire lumen located therein--within the blood vessel. However, this method of deflecting the ablation area works against the course of the guidewire, thereby inhibiting the ability of the catheter to continue to be inserted and/or manipulated while the balloon is inflated. Additionally, this deflecting method does not permit the distal ends of the optical fibers to be aimed outside the diameter of the distal end of the catheter.
U.S. Pat. No. 5,176,674 to Hoffman and U.S. Pat. No. 4,790,310 to Ginsburg each disclose a laser catheter wherein the distal ends of the optical fibers are deflectable beyond the diameter of the catheter. Therefore, these devices enable light energy to be selectively directed over an area that is larger than the diameter at the distal end of the catheter, thereby increasing the size of the cut made by the catheter. In these devices, however, the fluence over the ablation area does not remain constant as the distal ends of the optical fibers are deflected. This is because the optical fibers in the bundle of fibers at the distal end of the catheter spread apart from one another during deflection, thus increasing the size of the ablation area while the magnitude of the light energy remains constant.
U.S. Pat. Nos. 5,941,108; 4,800,876; and 4,784,132 to Fox and U.S. Pat. No. 4,875,897 to Lee disclose a catheter having a bundle of optical fibers that are deflectable at the distal end such that the fluence remains constant. In these devices, the bundle of optical fibers at the distal end of the catheter are shifted by at least one balloon positioned between the optical fibers and the wall of the catheter. However, the bundle of fibers can only be moved within an area defined by the cross-sectional area of the distal end of the catheter when the balloon is not expanded. That is, the ablation area cannot be deflected outside the diameter of the catheter. Therefore, in order to ablate a large obstruction, a catheter having a relatively large diameter and/or an inflatable balloon at the exterior of the catheter to move the catheter within the vessel is necessary.
U.S. Pat. No. 5,066,292 to Muller discloses a laser catheter having three distinct groups of optical fibers. Each group of optical fibers defines an ablation area at the distal end of the catheter. The three groups of optical fibers are concentrically located at the distal end of the catheter and separated from one another by an elastic intermediate zone. Each of the three groups of optical fibers are deflectable beyond the diameter of the catheter by inflating a balloon centrally located within the catheter, which, when inflated, causes the elastic intermediate zones between the groups of optical fibers to expand. The individual optical fibers in each group of optical fibers are rigidly connected to one another so that the fluence over the ablation area defined by each group of optical fibers does not decrease during deflection. However, because the three separate bundles of optical fiber spread apart from one another, the fluence over the entire ablation area at the distal end of the catheter does not remain constant during deflection.
Muller also discloses cutting off the light energy from two of the three groups of optical fibers so that only one group of optical fibers is used to ablate the tissue. Doing so, however, results in an inefficient use of the limited space within a blood vessel by the catheter. As discussed above, it is desirable that vascular catheters have as small a diameter as possible. When only one ablation area is used in the Muller device, the remaining portions of the catheter, including the two unused groups of optical fibers serve no purpose, thereby unnecessarily increasing the diameter of the catheter so that the catheter is unable to pass through small vessels.